The present invention relates generally to the art of completing subterranean wells having lateral bores extending from parent bores thereof and, in a preferred embodiment thereof, more particularly provides apparatus and associated methods for reentering the parent bores after the lateral bores have been cased.
It is well known in the art of drilling subterranean wells to form a parent bore into the earth and then to form one or more bores extending laterally therefrom. Generally, the parent bore is first cased and cemented, and then a tool known as a whipstock is positioned in the parent bore casing. The whipstock is specially configured to deflect a drill bit in a desired direction for forming a lateral bore. The drill bit is then lowered into the parent bore suspended from drill pipe and is radially outwardly deflected by the whipstock to drill a window in the parent bore casing and cement. Directional drilling techniques may then be employed to direct further drilling of the lateral bore as desired.
The lateral bore is then cased by inserting a tubular liner from the parent bore, through the window previously cut in the parent bore casing and cement, and then into the lateral bore. In a typical lateral bore casing operation, the liner extends somewhat upwardly into the parent bore casing and through the window when the casing operation is finished. In this way, an overlap is achieved wherein the lateral bore liner is received in the parent bore casing above the window.
The lateral bore liner is then cemented in place by forcing cement between the liner and the lateral bore. The cement is typically also forced between the liner and the window, and between the liner and the parent bore casing where they overlap. The cement provides a seal between the liner, the parent bore casing, the window, and the lateral bore.
It will be readily appreciated that because the liner overlaps the parent bore casing above the window, extends radially outward through the window, and is cemented in place, that access to the parent bore below the liner is prevented at this point. In order to gain access to the parent bore below the liner, an opening must be provided through the liner. However, since the liner is extending radially outwardly and downwardly from the parent bore, cutting an opening into the sloping inner surface of the liner is a difficult proposition at best.
Several apparatus and methods for cutting the opening through the liner to gain access to the lower portion of the parent bore have been previously proposed. Each of these, however, has one or more disadvantages which make its use inconvenient or uneconomical. Some of these disadvantages include inaccurate positioning and orienting of the opening to be cut, complexity in setting and releasing portions of the apparatus, undesirable torque-created rotational shifting of the apparatus, and danger of leaving portions of the apparatus in the well necessitating a subsequent fishing operation.
From the foregoing, it can be seen that it would be quite desirable to provide improved apparatus and methods for gaining access to the lower portion of the parent wellbore which are convenient and economical to use, which provide accurate positioning and orienting of the opening to be cut, which has setting and release reliability, is not complex to set and release, and which reduces the danger of leaving portions of the apparatus in the well. It is accordingly an object of the present invention to provide such improved apparatus and associated methods for completing a subterranean well.